In signal modulation and demodulation, a relationship between signals is usually represented directly by means of a constellation diagram. For example, a code element containing communication information is mapped to a constellation point in the constellation diagram in the modulation process, and a received signal is judged in the constellation diagram to acquire the communication information or the like in the demodulation process.
A constellation diagram has the following characteristics:
(1). Bits of different constellation points on the constellation diagram for modulation mapping have different reliability. For example, if bit x of constellation point A is the same as all or most of bits x of constellation points around constellation point A, bit x of constellation point A in decoding has a low error probability, i.e. high reliability; otherwise, reliability is low.
(2). When each of the constellation points includes more bits, different bits also correspond to different reliability. For example, a constellation point in a 64 Quadrature Amplitude Modulation (QAM) constellation diagram includes 6 bits, and reliability of the 6 bits may sequentially be “high, high, medium, medium, low and low.”
Therefore, if modulation symbols formed during multi-element code mapping are all mapped to low-reliability positions of constellation points, a poor anti-interference capability may be incurred due to low reliability. In addition, smaller errors in a transmission process may result in decoding errors. Meanwhile, there will be the problem of high error rate, which further results in low communication performance.
In addition, it is common to combine a multi-element error correcting code and high-order modulation in a conventional communication system to increase a data transmission rate and improve a sudden error resisting capability in a fading channel. However, modulation symbols formed by code element mapping may be unlikely to be recovered during decoding on a receiving side if there is deep attenuation for modulation symbols, namely when signals are seriously attenuated, in the transmission process, which may cause a high information transmission error rate and performance loss.
From the above, it is a problem urgent to be solved in a conventional art to provide a modulation mapping method capable of solving low reliability caused by deep attenuation and the characteristic of reliability unbalance of constellation points.